1. Field of the Invention
The present invention relates to an internal combustion engine.
2. Description of Background Art
An internal combustion engine is known that includes a structure wherein an oil supply passage extends across a cylinder block and a cylinder head branches at a wall portion of the cylinder head into an oil supply passage communicating with a support portion of a rocker shaft with an oil supply passage communicating with a support portion of a camshaft. See, for example, Japanese Patent Application Publication No. 2009-215923.
An internal combustion engine according to Japanese Patent Application Publication No. 2009-215923 is a diesel engine and a fuel injection valve is attached to communicate with a substantial center (top portion) of each of combustion chambers. This internal combustion engine is a four-valve engine with multiple intake and exhaust valves and multiple intake and exhaust rocker arms arranged side by side in an axial direction of each of the camshafts.
In the internal combustion engine, a space for forming the oil supply passage is limited because the shape of the cylinder head is complex and multiple members are provided in the cylinder head. Accordingly, when an oil supply passage capable of securing a sufficient amount of lubricating oil for the rocker shaft and the camshaft is to be formed, the oil supply passage becomes complicated and the passage length becomes long. The wall portion of the cylinder head needs to be made thick to secure the space for forming the oil supply passage. The internal combustion engine thus has a problem wherein it is difficult to secure a sufficient amount of lubricating oil and to reduce the size and the like at the same time.
More specifically, as in Japanese Patent Application Publication No. 2009-215923, when the internal combustion engine has a configuration in which the fuel injection valve is attached to the substantial center of the combustion chamber and the multiple rocker arms and the like are provided side by side in the axial direction of the camshaft, the oil supply passage branches to extend to a bearing portion of the camshaft and four points in support portions of the intake and exhaust rocker shafts located on both sides of the bearing portion in the axial direction of the camshaft. The oil supply passage is thus complicated and is long depending on portions to which the oil is supplied. The support portions of the rocker shafts are relatively thick in the axial direction of the camshaft.
Furthermore, although the internal combustion engine of Japanese Patent Application Publication No. 2009-215923 is a SOHC (Single OverHead Camshaft) engine, a DOHC (Double OverHead Camshaft) the engine requires that the oil supply passage should be formed while avoiding the fuel injection valve or a similar measure needs to be taken. Accordingly, the oil supply passage may become more complicated.
In an internal combustion engine using gasoline as fuel, an ignition plug is generally provided at the aforementioned position where the fuel injection valve is attached. As in the aforementioned diesel engine, this case also has a problem wherein it is difficult to secure a sufficient amount of lubricating oil and to reduce the size and the like at the same time when an oil supply passage capable of securing a sufficient amount of lubricating oil for the rocker shaft and the camshaft is formed.